Anti-Solvent-Free Fabrication of All-Inorganic Perovskite Films by Controlling Crystallization Dynamics

All-inorganic perovskite solar cells (PSCs) have gained considerable attention for their excellent thermal stability compared with conventional organo-metal halide PSCs. Among the various all-inorganic compositions, CsPbI2Br stands out as a promising candidate because it offers an optimal balance between thermal stability and photovoltaic properties. However, the device performance of CsPbI2Br-based PSCs remains markedly low because it is difficult to control film quality due to their limited solubility and rapid crystallization rate. Herein, we show that 2,3,4,5-tetrahydrothiophene-1,1-dioxide (sulfolane) effectively controls the crystallization dynamics when introduced as an additive into the CsPbI2Br precursor solution. This mechanism was confirmed by in situ real-time X-ray measurements during the crystallization process. Fourier-Transform Infrared Spectroscopy (FTIR) analysis also supported the retarded crystallization of CsPbI2Br by regulating the coordination environment between Cs+ and DMSO by sulfolane. As a result, we successfully obtained high-quality perovskite film with reduced trap density and pinholes even under an anti-solvent-free process. To the best of our knowledge, this is the first demonstration of anti-solvent-free CsPbI2Br-based PSCs (excluding vacuum processes), offering a significantly simplified fabrication route without compromising device performance. The optimized devices with sulfolane achieved a power conversion efficiency (PCE) of 12.16%, representing an enhancement of ∼28.1% compared to control devices. These results demonstrate that sulfolane is an effective additive for controlling crystallization dynamics in anti-solvent-free CsPbI2Br-based PSCs, which is a powerful strategy for commercialization of perovskite photovoltaics.